For those of you unfamiliar with Karin’s work, she is a researcher at the Laboratory of Apiculture and Social Insects (LASI) at the University of Sussex. This is the largest research group in the UK studying honey bees and other social insects. She also works as an ecologist with her husband Steve Alton at their company FlowerScapes, selling wildlife seed mixes and advising organisations on beautiful habitat creation and wildlife gardening solutions informed by the latest ecological research. You can follow her on Twitter at @KarinAlton.

So Karin certainly knows her stuff. But she really shook up us beekeepers when she posted the following advice on Facebook:

“hello! Latest research results from LASI indicate that between the dates of 10th december and christmas is the optimal time for oxalic acid treatment. Please check for sealed brood and destroy any, say, 48 hours before applying acid.”

Eek! We were all unsettled. Since I have started learning beekeeping the advice I’ve been given has been to apply oxalic acid as close to the winter solstice as possible (December 21-22), as that is when a bee colony in the UK is thought most likely to be broodless. And the older experienced beekeepers who I’ve learnt from drizzle that oxalic over as quickly as possible before whipping the roof back on.

Emma treating our hive with oxalic acid

So based on LASI’s research, Karin is proposing two revolutionary things:

1) The best time to treat with oxalic is as early as 10th December up to Christmas 2) Sealed brood should be destroyed a day or two before applying the acid

Of course we all had lots of questions for her, and there are currently 55 comments on the post. Some further explanation and advice from Karin:

“it’s a fallacy that you can’t very quickly check for brood, we have opened hundreds of hives (very quickly- talking here couple of seconds) without any probs, even in cold, snowy January.”

“if you want to use oxalic acid, you MUST destroy brood before, as varroa hide in sealed brood, so waste of time and money putting OA on”

“Between 10th dec to 24th [in the UK] is the time with least likely/fewest sealed brood. uncap brood 48 hours before application, you would not need to pull out every frame, in fact you can tell by shifting the frames slightly if there is any, should be very few. if you use dribble method, you dont pull frames out anyway.”

I asked about timings, as me and Emma can only really get to the hives at the weekend, and Karin suggested that:

“Emily, may I suggest you pop to your hive first thing Saturday morning, and work fast, you don’t pull every frame out, but first take outside frame out, move others one at time, should be easy to check without waving them about in fresh air.

Start from middle frame, most likely here may be a small patch of brood, uncap with hive tool, quick slide check of other frames, then lid back on. On Sunday afternoon, take lid off, quick look to see the bees didn’t recap brood, then dribble OA. If you cannot do this procedure, use other varroa method. As I already have said, no point exposing bees to another chemical, if you leave Varroa in sealed brood! Hope this helps.”

As Karin says, “The research is being written up. All I can do is to inform you our findings, what you choose to do with this info is of course entirely up to you.” She also advises that fumigation is by far the best method, as the vapour permeates the frames. You just need the right equipment, especially a good quality mask.

The National Bee Unit currently offers limited guidance on oxalic acid in their Managing varroa booklet: “Ideally needs broodless conditions; 90% average efficacy possible; sugarless solutions have poor efficacy; danger of significant colony weakening; more scientific trials needed; highly toxic by inhalation, ingestion or skin absorption”. I think part of the reason for the limited printed advice is that the legal position relating to the use of what are termed ‘generic naturally occurring substances’ such as oxalic acid is complex. Generally the NBU inspectors are willing to give more advice on it in person.

What do you think, is destroying sealed brood a tactic you’re willing to try? I must admit I’m a bit nervous about it, even though I can see the benefits of destroying every last one of those mites. I think part of the reason for that is that I want to nurture life rather than destroy it. But then again we destroy brood during the shook-swarm in spring, and the bees bounce back strongly from that.

I’ve written a few posts before featuring advice from Karin, she is a no-nonsense lady who always has plenty to say:

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About Emily Scott

I am a UK beekeeper who has recently moved from London to windswept, wet Cornwall. I first started keeping bees in the Ealing Beekeepers Association’s local apiary in 2008, when I created this blog as a record for myself of my various beekeeping related disasters and - hopefully! - future successes.

Emily, I too am troubled by this advice. FWIW, I would not follow the instructions to destroy sealed brood. Yes, that means you will not achieve a 100% mite kill…and research, which measures % mite kill, implies that 100% per treatment is both achievable and optimal. I don’t think in this case that 100% kill is optimal. It will be enough to knock down the phoretic mites as most of the mites will, thanks to low brood volume, be on the bees. Not every sealed brood has a mite sealed in with it, and you can hope your girls have detected infested brood and have disposed of at least some. So the brood infestation quotient should be small. Remember too that vapour crystallizes onto the frames and so there will be a miticide action until those crystals evaporate completely…so the emerging brood gets a small dose of oxalic acid that way. You can further reduce infestation levels by repeating the vapourization treatment at weekly intervals as the cohort of sealed brood hatches. I would rather leave an essential oil laced grease patty on the hive and do one midwinter oxalic vapour treatment and leave it at that. The bees can handle low mite volumes…and regrettably until we eradicate the Varroa, any colonies that can’t handle low volumes of mites need to be weeded out of the bee population anyway.

Hi Janet, thanks for your comment. I think if using vapour treatment there is no need to destroy the brood… but relatively few beekeepers I know use the vapour treatment. By far the most popular method is drizzling, probably because it’s simpler, fast and requires less equipment. I’ll be looking more seriously into vaporisation now… maybe too late for this year but could get everything ready for next year. From what I’ve read one treatment per winter is preferable, as repeated treatments could be toxic for the bees?

Not sure that most of the mites will be phoretic if brood if present. They are very attracted to brood so may pile into it in large numbers? Also, not all honey bees detect infested brood. The varroa are very good at hiding under the larvae so that the bees don’t know they’re there. A female mite will enter an uncapped cell with a larvae inside and bury herself under the larval food, where the bees – and beekeepers – can’t see her whilst inspecting. She uses specialised tubes to breathe during this time. A pheromone is given off by larvae ready to be capped – female mites sense this earlier than adult bees and receive a cue to enter cells just before they are ready for capping.

It does worry me that the bees might feel despondent from the destroyed brood, and also trouble themselves trying to remove it, breaking up the cluster in doing so.

All good points. Doug Brown has a Youtube video titled “2012 10 Oxalic acid vaporizer (JB200) for honey bee mite control” that you may find interesting. I have ordered this small, easy to use vapourizer. I like the fact you do not have to open the hive (which among other things breaks all the propolis seals, and in the cold the bees will not be able to break cluster and reseal). I also like no wet bees, no breaking cluster, no residual effects on larvae. Some bees do detect the mites in the sealed brood and remove the larvae, so I hope the girls are that sort! I join you in being unhappy at varroa in the hive, and especially at the bee:mite ratio in winter. But I cannot help feel pushing for 100% kill is the kind of approach that is as fraught at the condition it tries to remedy.

A great account of the discussion Emily. I’ve made a few enquiries and posted this on the FB page just to put the brood destruction issue into perspective. “Hasan Mohammad Al Toufailia’s research has shown that mid-winter OA treatment is most effective when brood has been removed. His research also found that 90% of colonies are naturally broodless in the time before Xmas, with the Queen recommencing egg-laying in early January. These colonies will benefit fully from either trickling or sublimation, and of course there will be no need for brood destruction. The key point being that in the Sussex colonies used in this research, 90% were already broodless.

Broodlessness varies I suspect across the country. A lesser (or absent) broodless period in central London colonies maybe? More pronounced as you go up the country?”

My problem with the debate wasn’t the brood removal issue (which really isn’t a surprise), it was the incompleteness of the original posting and the lack of response to the very real questions raised.

Hi Bill, that’s great news that 90% of colonies Hasan found were naturally brood less at that time. I would be overjoyed to check and not find any brood to destroy. For once I find myself wishing for some really cold weather! Trouble is London is always a few degrees warmer than the surrounding countryside.

It is, part of the reason I wanted to post about it here was to try and get a wider audience for this information, as not everyone’s on Facebook. I’m very glad that we have scientists spending time trying to improve bee health.

The whole thing seems extreme to me- the opening a hive in the middle of winter, gassing the hive with oxalic vapor, killing brood frames… I dunno this doesn’t seem like a way to keep bees, alive or otherwise. I know the popular opinion is to battle varroa with whatever means necessary and I was under the impression that oxalic acid was meant to be less harmful to bees but it seems that if you are destroying frames of brood, cracking open hives in cold weather you might actually be part of the problem, not the solution.

I know what you mean – but if using the vaporisation technique we wouldn’t need to open the hives. The research done on multiple colonies indicates that they cope well with it and are healthier for it.

The Asian honeybee has lived with varroa for probably millions of years, which is how it’s evolved to cope with it. None of us beekeepers have that kind of time on our hands. Man has yet again messed with the natural order of things and brought over a parasite which our European honeybees have not yet evolved high defences against and probably won’t for at least hundreds of years. Emma and I only have four hives and they mean a lot to us, so we want to give them every chance possible to survive.

I know there are people working on breeding for varroa resistant bees. I have heard one of our National Bee Unit inspectors say that good husbandry methods, combined with requeening each year with a resistant-bred queen from specialist breeders, produces this effect. But it’s not sustainable when queens are mating with local drones from all over the place, and therefore resistant bees are going to take a long time to do significant good for beekeeping. Do I want to start importing a queen each year from a breeder abroad, breeding queens used to a completely different climate? Not really.

Emily,
I thoroughly read the exchange on the LBA page and you’ll have to forgive my incredulous response above, but viewing the debate as a treatment free beekeeper that wouldn’t open a hive in mid-winter much less chill brood intentionally, the methods described seem nothing short of draconian. Still, the entire method wouldn’t be available in my climate anyhow as there is not natural brood break big enough to even risk destroying brood. Its hard for me to fathom that opening a hive in freezing weather to break up the brood nest in order to expose them to oxalic acid as a proper management procedure. Still, it sounds as if several people are willing to take it seriously so I guess time will tell, no?

I’m beginning a three year study to determine a developed natural resistance to varroa in local populations of feral-sourced bees. It’s commonly thought, anecdotally, that our local bees have some strong natural resistance to long term exposure to varroa and some hives I have seem to bear this out. I am a bee remover as well, so I do see quite a few multi-year hives that have never been treated that appear to have found some sort of balance with varroa. Still, anecdotal evidence isn’t proof, and the study is meant not just to determine resistance but develop a strain of localized bees that exhibit strong hygienic behavior that can also be commercially viable. This already exists in some newer strains of bees here in the US but not in my area of Southern California.

There is a Finnish beekeeper that had spent the better part of a decade not treating and developing his own line of varroa resistant bees (Julani Buckfast) which are now sold to various beekeepers around Europe. Here’s his observations and report. He’s an acolyte of Brother Adam.

You do have a good point about localized bees, perhaps there are breeders in the UK that have a desire to breed resistant bees?

Thanks Tyson, the link is intriguing. I like that Julani is honest and admits “I have had some fears, that inbreeding is slowly having an impact on our stock.” This tells me that he must presumably be in a quite remote area? In the UK breeders are really up against it because not only is the UK a densely populated country with hives everywhere, our weather is not suited to queen breeding.

The biggest problem in my beekeeping lately has been the horrible cold and rainy summer we have had for the last three summers now.
Our bees have changed. They make smaller colonies and develop much more slowly. Infestations vary, this year average around 4%. Bees take out brood and to me, varroa is no longer an issue.
Cold weather. To get idea how cold two examples:
– I have been a beekeeper 40 years. And never before 2016 have I heard a beekeeper say he got no honey at all.
-Barley harvesting starts here usually Mid August. Year 2017 it started in mid September. Some farmer have not even started yet today 29.9. Why? Because it is not ripe, there simply has not been enough warmth.

Now when three things are combined, cold weather, slowly developing bees and mites which prefer drones if they can, the result is poor free matings or no matings at all!
I have had to start inseminating almost all my queens. I get better results with inseminated queen than free mating.

There is a big queen and bees massproducer in Southern Italy with whom we have started cooperation. More later about that.

Thanks very much for your comment Juhani. I wonder if climate change is behind the increased cold. I hope things improve for you. You’re obviously an extremely skilled beekeeper if you can successfully achieve insemination. At least the smaller colony size and hygienic behaviour is helping with varroa!

Thanks for reminding me! That study plan fell apart from lack of resources, namely bee yard space. I recently got my first apiary which is difficult to find in this built-up area (Los Angeles). I’ve been working this year to build it up and clear the land, and next year I’ll be doing comparison monitoring between our local resistant feral bee population and some VSH local Italians that I’ve been requeening with. The feral population fare better than the VSH Italians against varroa, but can be unmanagable Africanized honey bees. The same traits that lead to resistance seem to be bundled up with defensive response. I’ll be open breeding the selected calm feral queens with the VSH Italians, hopefully to achieve some kind of workable balance.

Sorry to hear of your climate problems, ours is frequent and debilitating drought. We seem to be in a cycle of one good rain year and 5 bad ones, but everything is in flux so who knows where we’ll be in a decade.

Sounds like good stuff, good luck with the breeding. It’s fascinating to hear the different advantages and challenges other beekeepers around the world face. I’ve visited California and seen the water problems you guys have. Whereas here in Cornwall the rain virtually never stops!

Hi Emily interesting post and spotted people talking about it elsewhere on an internet forum and wondered where it originated.

You may not be surprised to know that I don’t like the idea of removing frames and then killing any brood at this time of year. I have only used oxalic once in seven years and have found that the levels of varroa throughout the following year are acceptable and not out of control. To me the trick is correct Thymol treatments in late summer. We have to balance treatments when needed and other times let the bees be bees. Oxalic acid is a good treatment if needed but only if needed.

I realise that the association apiary has to be treated with oxalic regardless and not looking forward to it but breaking up any cluster by removing frames will in my opinion be a bad move and damage the bees beyond what the few varroa left behind could ever do.

Vaporizing oxalic is not new and more people are doing it these days. It can be achieved with little homemade equipment and a blowtorch but with less control on the correct temperature required or with a few more expensive accurate delivery methods that require a generator or car batteries to operate. But one thing that should not be overlooked is the gas is very bad for the beekeeper and a quality face mask that can deal with gas vapours should be worn regardless of application method.

Thanks Tom. Instinctively I don’t like the idea of destroying brood, but on the other hand the scientific evidence seems to suggest it could benefit the bees in the long run. My hope would be to find that there is not any brood present when we do the treatment.

I’m going to ask the committee what they think about buying some equipment in from the association. Maybe we could get someone who’s used to doing the vapour method to do us a talk about it.

Really liking your blog, will read it properly tomorrow when I’m feeling less sleepy. Can see there’s some interesting looking equipment and cute swan pics, your boat looks very cosy.

That’s an excellent idea regarding a talk on vaporising oxalic and we could do with the odd talk from time to time and it will be interesting to see what the committee will say regarding spending some money.

A bit more information regarding this culling brood prior to oxalic cropped up on the beekeeping forum. I did have a hand in it following your blog and the first few pages are just typical forum arguments but some more information did surface. http://www.beekeepingforum.co.uk/showthread.php?t=27337

Thanks for the comments regarding my blog early days just settling down but good fun.

There is a nice article on breeding up varroa resistant bees called “Producing Varroa-Tolerant Honey Bees from Locally Adapted Stock: A Recipe* “. In just two or three years, by setting up an entire apiary of colonies that receive no varroa treatment, and breeding ONLY from the survivors, resistant stock was produced. This approach, while successful, requires land, money (in terms of bees and equipment) and some time. I am trying to find a land partner in our municipality; IMHO, while we wait for the silver varroa bullet, every bee club should be running a survivor bee breeding project like this, distributing the resulting resistant bees to all members, saturating local areas with varroa resistant genes. I explored that idea in a blog post, http://planbeeproject.wordpress.com/2013/04/06/welcome-to-2013/

Thank you, this is exactly what I’m attempting. I need a data set to demonstrate one point, then use that data set to develop resistant local stock. I agree that rather than continuing to perpetuate the cycle of treatment tolerance that has been the norm for the last 30 years, we should be focusing on independence from treatments altogether. It doesn’t take decades to achieve this, I’m sure of that.

It’s an interesting idea, but I don’t see how it can be done without a co-ordinated effort amongst beekeepers to only use these “resistant” queens, otherwise the next generation of queens will just mate with all sorts of drones. Probably beekeepers would have to keep buying in queens to preserve the varroa resistant effect. My worry would be that such a project could reduce the genetic diversity of our bees, which is likely to leave them more vulnerable to other problems.

Emily, you describe most eloquently the rock and the hard place between which we beekeepers find ourselves! Here in BC we are flooded with NZ packages yearly, meaning most local drones are new to the area, unadapted and intolerant of varroa. The NZ bees are great, don’t get me wrong! We absolutely depend on them to replace winter losses and for expansion and new beeks. But this also means every year we fill the local bee gene pool with unadapted genes. A lot of us are trying to get survivor projects running. There are varying lines of varroa tolerant bees out there that can be brought in to increase genetic diversity….not many but some. I suspect the gene pool is limited everywhere thanks to the bottleneck of the varroa/tracheal mite impacts in the late ’80/’90’s, and the widespread use of poor quality commercial queens (mated to few drones). Mercifully more attention is being paid to making sure queens are very well mated now. Like yours our climate is not optimal for queen breeding as it is in the southern USA. But! While we cannot bring off multiple waves of queens each season, we do have a nice June/July window to breed up wild mated queens that can be overwintered and sold the next season either alone or with the nucs/singles they wintered in. To this end I try to acquire bees from varied and promising sources. Half measures, yes, but all I have!

I’ve never heard of oxalic acid before, but killing off brood this late in the season sounds ridiculous, and a far more drastic measure than one I would be comfortable taking. However I’m curious enough to start looking around to learn more about this type of treatment. Thanks for bringing it up!

Oxalic acid is a common anti-varroa treatment here. It occurs naturally in some plants like rhubarb and works by burning the feet of the mites, loosening their grip on the back of the adult bees. Only one treatment needs to be done per winter.

Other beekeepers who’ve been applying oxalic acid this month have said they’ve found no brood in their hives, so I’m hoping there will be no need to kill any when we do the treatment.

Hi Emily
I am sure you are not surprised to learn that I consider this an exceptionally invasive treatment of bees at a most vulnerable time of year. In all likelihood, bees can withstand a few brisk frame inspections but why do it? Then again they can tolerate a certain level of mites. Nothing eradicates varroa 100%. There is always going to be wastage of treatment. It’s a nice goal, but if it means more invasion of hives for incremental gain at best then I will pass.

I completely understand how you feel. I am torn but think I’ll wait to see what the research says when its published and how other people’s hives cope with the brood destruction. Some London beekeepers have discovered no brood in their hives this December, so it may be that there’s none to destroy anyway.

Great blog post – great discussion. Me? I wouldn’t open a hive here (NW Washington state, US) in December. One note : like westernwilson, I raise queens in a climate similar to yours, and the best queen breeder I know is 60 miles south of me (same miserable weather). Try it – you’ll wind up with queens suited to your climate. And yes, you do have to coordinate with all (ok most) beekeepers within 3 miles of your virgin yard. Again thank you for a great post…

Thanks Karen. I follow another beekeeper in western Washington state (http://batelsbees.wordpress.com) and get the impression your weather is even wetter and colder than ours here. We do let our bees produce new queens, but we have no idea what drones they mate with unfortunately. Co-ordinating to restrict the gene pool of drones available in London would be absolutely impossible!

Emily, I was telling my beekeeping mentor about your post, and we did think that in an age where few or no ferals are out there, if every colony in an area received this kind of treatment, and nearly 100% mite kill, there should be an area wide reduction in mite numbers as drone transmission would be so low….

Hmmm…not so sure about that Emily! : )
But I am doing a vapour treatment next week. There are so many pollination service hives flooding our area during blueberry bloom, I have no incentive to go for that 100% kill (drone drift will reinfect me no matter what). Knocking them down is enough.

Emily, I do have a question for you! In the case of the beekeepers who found that 90% of the colonies sampled this time of year had NO brood….did they examine the brood in the 10% that did have capped brood?? I would be very, very interested to know what the mite infestation rates were in that brood. When I examined drone brood this summer that was sacrificial brood, the level of mite infestation was 10-20%, and was likely vanishingly small in worker brood. While I would expect midwinter (worker) brood to be much more heavily infested (being the only game in town), I wonder just how infested it is. It seems a shame to eradicate the healthy brood, and from what I have read, lots of bees detect heavily infested brood and get rid of it anyway. These bees hatching now are the foragers in March, when our first pollen and nectar blooms begin. Those March bees are supporting the brood that will itself be nursing the all-important April eggs/brood. I’d like to see a study done on brood breaks throughout the year, and how their timing impacts honey yields!

To answer your question you’d be best off trying to contact the LASI Phd student who has been doing the research I think, Hasan Mohammad Al Toufailia. If you take a look here, his email address is on the page: http://www.sussex.ac.uk/lasi/aboutus/people.

I agree that the winter brood is really important, especially as so few young bees will be produced over winter. But the brood would only be eradicated that one time before oxalic acid treatment, so the queen would have a chance to lay more eggs straight afterwards. A couple of London beekeepers have checked for brood this week and reported on the London Beekeepers Facebook page that they found none, so lots of the colonies are doing their own natural brood breaks anyway.

I’m really interested in the new research and keen that research continues into bees and bee diseases. However, being already uncomfortable opening the hive in December to give oxalic acid I’d be reluctant to do a ‘brief’ inspection and destroy any sealed brood this time of year. As you know I’m less sentimental about saving every bee (having observed the unsentimental and practical nature of bees over past four years in protecting the good of the colony) and more concerned with saving colonies. Fumigation equipment that allows treatment without opening the hive sounds preferable, then cull the old brood in a shook swarm in spring when the bees are able to build up again. In London it is harder to be natural and treatment free, but this sounds at least like an approach that works with the bees’ natural cycle rather than against it. You’re right that humans did introduce varroa to the European honeybee but I wonder if we are doing harm again by a human approach to eradication. I’ve noticed less problems with our colonies and varroa in past two years and wonder if we need to be more patient and keep varroa at controllable levels while working with the bees to adapt to this mite, rather than 100% varroa eradication approach that is also harmful to bees. Is it humans or bees who are concerned with 100% eradication. Also I would be interested in more research on nosema and other diseases transmitted or escalated by varroa, which often seem more deadly to bees than the mite itself!

Hi Emma, I understand not wanting to destroy the brood, I’m not keen on it either. The good news is that some London beekeepers inspecting this December as a result of Karin’s comments have been finding their colonies are broodless anyway.

I brought up the idea of buying fumigation equipment for the apiary at the AGM, but Pat and John are against the idea as they say it’s too much of a safety hazard and the equipment is heavy to lug around.

That’s a shame about fumigation equipment, although I can understand concerns about safety risks – it would be difficult for the association to monitor and take responsibility for that. I suppose it will depend on the long-term results like improved outcomes of colonies treated with oxalic acid with brood destroyed compared to colonies treated only with oxalic acid, then weighing against risks/benefits of winter inspections and disrupting the cluster – we’ll have to wait and see. I’ll be interested to read the published research and reviews of it. Always so much reading to do in bee-land.

I am a relatively new beekeeper but I have some experience using oxalic acid vaporization against varroa. It is very effective and does not harm the bees or the brood. Last autumn I had a major varroa infestation ( 24hr drop > 100 ). I treated with 6 treatments 5 days apart no harm to bees, brood or myself. After a followup treatment just after Christmas I have only seen one varroa on the bottom board and now have a thriving hive. I posted about this here http://beekeepingnaturally.co.uk/varroa-mite-treatment-using-oxalic-acid-vaporization

I really cannot see the benefit in culling brood and opening up the cluster – it is simply over invasive and in my view the idea shows wrong thinking. Oxalic Acid is not 100% effective on mites, so even killing all the brood and treating just the bees will not remove all the mites or reduce the risk of re-infection from drones in the spring. I just question what she is trying to achieve.

Thanks for your comment – I love your blog! Is there a way to sign up to it via email? I’ve stopped using RSS readers.

Research does seem to indicate that vaporisation is the most effective way of treating with oxalic acid. I’ve tried to persuade my local association to buy a communal vaporisation kit, but they are against the idea for practical reasons of it being more time consuming than drizzling and also health and safety reasons.

Rather than destroying the brood I plan to do the oxalic acid when the colony is broodless if possible from now on – this actually seems to be most likely to be early-mid December, as Karin said. Her advice is based on research the LASI team has carried out, so there is data to back it up.

Looking forward to seeing the research, I must admit to being slightly sceptical. Physical location, type of bees, the changeable weather and of course the very act of observing the bees will add variables that will certainly be a challenge.